This invention pertains to a pipe machining apparatus and, more particularly, to such apparatus that can be mounted externally of a pipe and which causes one or more tool heads to revolve about the pipe with a tool head having a tool slide which may be advanced toward the pipe to achieve a particular machining operation. An apparatus of this type requires a frame which can be easily and quickly mounted to the pipe and means for advancing the tool slide as the tool head revolves around the pipe. The invention relates to improvements in such structures.